Frank,

Your right the article did not claim a change in flame speed,though this statment confused me a bit.



Sure sounds like a flame speed, or an energy issue. I have not seen any showing that pump gas had any signifigant differance in either based on octane. Though I have seen economy differnaces caused by winter mix oxegenated fuels.

Kevin <img src="/forums/images/graemlins/cheers.gif" alt="" />

Kevin:

Thanks for the tips. I'm reassured to know that your MPG was once where mine is.

The one BIG thing that I need to do is get a rebuilt dizzy. Leterally everything else off of the donor had issues. I fell asleed at the keyboard and missed one on ebay recently. I want to get a used one and do the rebuild, then swap it in.

I also need to pull the OVCP and make sure the injectors are not leaking.

Regarding the DP, there is a shop on ebay selling T304 pipe for prices that are barely more than aluminized from JCW. Redoing the whole shebang in stainless is high on the list. (Right now I have my hodge-podge of 2.5" back of the DP, all in cheap steel.)

On the MAF, I was running the Quest air can. I then picked up a V6 can from a Raider. (The V6 can fits nicely.)Someone here (Okred I think)did the same and thought it performed better. Right before the swap, I had one tankful of good MPG- something in the high 15s. Then I made the swap and was back to the lesser MPG. Last weekend I swapped the Quest MAF into the V6 can. I'll report back on how things go. BTW, it does feel a little bit weaker now.

Definitely have to rule out the injectors and dizzy, though.

I think what the author is trying to convey is that even after the mixture is lit, additional compression effect (from combustion) on the portion of the mixture not yet burned causes a delayed/extended burn relative to a lower octane content because - if the octane rating was lower, the developing combustion pressure would ignite the balance of the mixture faster.

Maybe he is saying it in a round about manner, but in any event, my eyes sure can't see it and I sure can't prove it one way or the other. <img src="/forums/images/graemlins/lol.gif" alt="" /> I'll leave that explanation to others. All I want to know is what works the best.

I do think the article makes a good suggestion to try a few brands to see if there's a noticeable change - something I'm guilty of never doing..... I usually go to the nearest Exxon station because (at least here) they went through a time of building a lot of new stations that were located on nearly every interchange and they had clean bathrooms. IIRC, my wife participated in the decision about which gas stations were the best. <img src="/forums/images/graemlins/wink.gif" alt="" />

Frank

I am not going to get into flame propagation as this can start a debate that can go on forever. Fuel octane may vary from day to day at any refinery. They are only required to meet the minimum for that octane. Add to the equation that at least in my area, where there are many refineries, the oil companyÆs will buy fuel from each other when production is shut down for repairs, maintenance etc. I have personally witnessed this many times. So if you are going to try different gasolines, you have no way of knowing that you will receive the same blend and octane consistently. The bottom line is that one pound of regular gasoline can deliver 20,460 BTUs of heat energy while High-octane gasoline actually has less heat energy potential, only 18,250 BTUs per pound. Choose what works for you.
Conner

Since we buy by the gallon and not the pound... How would that work out on ones wallet? Is one more dense than the other? any interesting links?

Chevron

I found some good info on Ethanol , MTBE and how they affect MPG, but nothing on BTU's vs octane an a quick search of refiners.

For sure the Federal winter blends hurt your MPG 2 -3%, and Cali gas is an automatic year round -3% mpg.

Kevin <img src="/forums/images/graemlins/cyclops.gif" alt="" />

Kevin, one of the statements on your Chevron link;

Thanks Winston,

I only gave that page a quick read at the top of the chart, I was on my way to work. That seems to confirm That there is not a significant difference in BTUÆs per gallon based on octane for pump gas that we can buy.

Not that we buy leaded but an example of how it can happen is adding lead in a small amount gives a large increase in octane but would not change the energy content noticeably. This same analogy would apply to BTUÆs per pound, take some 87 octane, add TEL till it hits 91, the density is not significantly changed but the octane is, therefore the BTUÆs per pound remains constant.

In other words, there are lots of ways to get high octane and depending on how you do it you can get more or less BTUÆs per gallon but there is not necessarily consistent correlation.

It seems the biggest factor is oxygenates to reduce smog / pollution. That explains my last experience on vacation. Once I got well out of California and got some real gas (non oxygenated) my fuel economy picked about 1.5 MPG up according to my cars MPG meter.

Seems to make sense to me.

Kevin C

Roughly 6 pounds per gallon.

Heat is what makes engines go. Therefore, the less heat (BTUs) the less go. The less go per gallon=lower MPG.

Higher octane resists detonation better.

Clay

Then some of these Monteros should get 100mpg..... <img src="/forums/images/graemlins/lol.gif" alt="" />

Sorry, couldn't resist. <img src="/forums/images/graemlins/ignore.gif" alt="" />

Frank

384.0 miles
20.144 gallons

19.06 mpg

Clay